"What are you doing?" you ask.
"Changing you back, of course. Unless you really want Gene to take you back to his dorm."
"I think I do," you say. "It seems very tempting and it's not as if he has a girlfriend already."
When you make that statement, Mike gets angry for some reason. "All right, you're changing back now." You don't understand exactly what made Mike upset at that idea but he says "I guess I can't blame you, it's not as if you even remember anything."
And you still don't understand it. But it couldn't hurt to change you back. Besides, you have an idea.
Mike turns the light to blue and says "Hold out your hand." You put your hand out and he puts the flashlight between your fingers and his.
"Gene, kiss me," you say.
"Sure, Erica. But what's all this stuff about changing?"
You let Gene put his arms around you and bring you close to kiss him. You put one arm on him and let the other free to be moved around by Mike. "Change me back, Mike," you say just before the kiss, and Mike moves the light over your body while you and him are both touching it. You aren't really watching what he's doing since you're busy kissing Gene, but the kiss is over by the time Mike aims the light towards your crotch at the end of the transformation. Since you remember being a guy with a pussy, you don't want him to change that, so before he can do anything, you snatch the light away from him and turn it off.
That was the idea. The flashlight changes reality but it doesn't move things. If you turned a guy into a girl inside a guy's locker room, she won't vanish and reappear in the girl's locker room--rather, the flashlight would invent a reason which explains why she's in a place where girls aren't supposed to be. If you're changed back to your normal self while Gene's kissing you, the flashlight won't break the kiss--there would be a new reality in which you're back to normal but Gene is still kissing you. In a reality where Gene is still kissing you, he probably still wants sex with you. So even though Mike thought that changing you back would prevent Gene from wanting sex with you, it didn't.
Of course you can't *know* that. Maybe in the new reality it was a dare or something.